Jeremy S. Cook


Do you need to know the temperature? What about the temperature for the last day or two in 15-minute increments? If so, then the RTemp device from Andrej Rolih could be just the thing. It uses a Nordic nRF51822 BLE SoC for communication, and a Sensirion SHT21 temperature and humidity sensor to survey the environment.

Logging-wise, the RTemp stores temperature and humidity measurements every 15 minutes, up to 254 measurements, which works out to be roughly 2 ½ days of info. To save space, temperature increments are only accurate to 0.5°C, and the lowest and highest temperatures are ±64°C. Time and date aren’t stored, so you’ll have to do a little estimation here.

The device can be used with a smartphone, and can be accessed on both Android and iOS via a BLE explorer, though there is an app specifically available for iOS if you so choose. The RTemp can also be used standalone, or integrated into a home automation system, and perhaps the coolest feature is that it is small enough to strap to the back of a AAA battery holder.

Given BLE’s power efficiency, this should mean a prolonged usage period between battery changes, and would be great as a device that can be implemented very quickly. Code and other needed build files are available on GitHub if you’d like to create your own.



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